The invention relates to a means for adjusting a rotor blade, the long axis of which extends out from the hub of a wind power plant rotor, about an azimuthal adjusting angle in relation to the long axis, and to a process for operating this means.
Controlling or regulating the azimuthal angle setting of the rotor blades of wind power plant rotors makes it possible to reduce the angle of incidence at high wind speeds. Thus the rotor speed and the power from the generator driven by the rotor can be limited, preventing overloading of the mechanical and electrical components of the wind power plant. Corresponding systems operated electrically or hydraulically have been known for many years. Those include systems with adjusting drives in the rotor hub or in a [LP] tubular section with a nonrotating connection to the rotor blade. Systems which are integrated directly into the rotor blade are also known (DE-A 196 34 059).
There are also partially redundant systems in which, for example, a collective hydraulic central adjusting means is combined with three individual hydraulic adjusting means installed in the rotor hub which individually cover only part of the adjustment range required at low-load operation. There are also occasional designs of fully redundant drive systems for rotor blade adjustment. Those, however, have no redundancy for the case of blocking of the rotating connection between the rotor blade and the rotor hub.
For example, if one of the rotor blades fails during a disconnection from the network or an emergency shutdown of the adjusting system, that rotor blade remains in its operating position, while the other rotor blades are adjusted into their braking positions. The resulting aerodynamic imbalance, especially for large rotors 100 m or more in size, leads to such high stresses that they represent the case of extreme load which must be taken into consideration in designing many major components of the turbine.
The invention is based on the objective of providing a means of the sort initially stated which assures reliability by complete redundancy while still allowing design savings on the entire wind power plant to make up for the added cost needed.
This objective is attained according to the invention by a means comprising two independent adjusting systems, each of which adjusts the rotor blade even if each of the other adjusting systems fails.
In the means according to the invention, the azimuthal adjusting movement of the rotor blade is made up of the adjusting movements of both the adjusting systems. As the two are independent of each other, if one of the two adjusting systems fails, the other one will still do the adjusting. The cost of this complete redundancy is more than compensated by a distinct reduction of the extreme loads which must be considered in dimensioning.
It is understood that one means according to the invention is provided for each rotor blade of the rotor. For examples, rotors with two or three rotor blades have, correspondingly, two or three means according to the invention. The drive energy for the adjusting system can be hydraulic, electrical, or mechanical in a known manner. The mechanical energy can, for example, utilize the rotational energy of the rotor. Energy storage can be provided independently for each means. Alternatively, a single energy store can be utilized jointly for all the rotor blades of a rotor. In any case, the drive energy can also be obtained from internal or external forces operating on each rotor blade, such as air, mass, inertial or centrifugal forces.
One suitable embodiment of the means has each of the two adjusting systems placed between the rotor hub and the rotor blade, with a rotatable coupling which can be adjusted by the drive. That can, for instance, be accomplished by adding the additional adjusting system to the adjusting system normally placed at the rotor hub. Alternatively, though, both adjusting systems can be placed outside the rotor hub, at a distance from it, along the longitudinal axis of the rotor blade. All the common [see Translator""s note 1] drive systems, such as electrical drives, hydraulic cylinders, screw spindles, and the like, are covered by the drive concept in this description and the claims.
It may be advantageous to place the two rotatable connections so that they are essentially concentric with each other. In this case, they have the same radial position with respect to the rotor axis. Then the flanges of the rotor blade and the rotor hub which connect to the rotatable connections can be made with clearly different diameters. Under certain conditions, such as limitations due to transport logistics, that can make an advantageous contribution to the economic optimization of the wind power plant.
With respect to a simple modular design, it is advantageous to place the two rotatable connections separated axially from each other along the long axis of the rotor blade, and particularly to place one of the two rotatable connections and its drive at the rotor hub and the other rotatable connection and its drive outside the rotor hub. In this case, the adjusting system at the rotor hub and the other, as a separate unit, are axially separated from each connecting flange of the rotor hub.
The structure is particularly simple if the rotatable connection outside the rotor hub and its drive are placed on a tubular part extending axially between the two rotatable connections. Then the tubular part can also be used to hold the drive energy store for the adjusting system. At the same time, the tubular part can be used to adapt the rotor diameter to different sites with the same rotor blade. The tubular parts of different lengths (extenders) needed for that can preferably be made of fibrous composite materials such as glass fiber reinforced or carbon fiber reinforced plastic. A winding process is preferably suited for that.
Another suitable embodiment has one of the two rotatable connections and its drive at the rotor hub and the other rotatable connection and its drive connected directly to the rotor blade. That is particularly suitable for high-wind sites at which a small rotor diameter is advantageous. The intermediate segment (extender) formed by the tubular part is omitted in this case. The drive for the rotatable connection on the rotor blade and other components connected with it can be placed either inside or outside the rotor blade.
It is specifically provided, as part of the invention, that the two adjusting systems can be actuated simultaneously. In that way, the adjusting speeds needed in a safety shutdown can be achieved with a particularly economical design of the means because the adjustment speeds are the sums of those for the individual adjusting systems. For example, consider a wind power plant having a three-blade rotor and in which the necessary adjusting speed is to be 7xc2x0/second. Thus this wind power plant has three adjusting means, each with two independent adjusting systems, for a total of six adjusting systems. As an example, three of them can be operated at a maximum adjusting rate of 3xc2x0/second with the other three at 4xc2x0/second. If the wind power plant is robustly dimensioned, it is adequate to equip the three adjusting systems with the lower adjustment rate with just one common drive and/or energy storage system (collective adjusting system), while the adjusting systems with the higher rates are designed completely independent of each other. In all, then, there are four completely independent adjusting systems. If a single adjusting system fails, then two rotor blades are driven at 7xc2x0/second and one at 3xc2x0/second. But if the collective system fails, then all three rotor blades are driven at 4xc2x0/second. Both types of failure produce substantially lower loads than is the case for the state of the technology, where blocking of one rotatable connection results in two rotor blades being adjusted at 7xc2x0/second while the third rotor blade does not move at all. For highly optimized wind power plants, however, it will be reasonable to make all the adjusting systems (six adjusting systems in the case of a rotor with three rotor blades) completely independent, so that the full adjusting rate is available at two rotor blades for any individual failure.
In another advantageous embodiment, the azimuthal adjustment rate resulting from the operation of the two adjusting systems is variably controllable. To reduce the load on the tower of a large wind turbine in a safety shutdown by a negative tower thrust (reverse thrust), it has proven very advantageous, when the safety chain is initiated, to adjust the rotor blades to their safe feathered position, not at a constant rate of adjustment but with an adjustment rate which can be varied during the adjustment process. Depending on the plant concept, depending, for instance, on the number of rotor blades, the rotor speed, and the compliance of the rotor blades and of the tower, it may be best to control the adjustment rate as a function of the time, of the rotor blade angle, or of the distance of adjustment.
Of course, the technical problem arises that the safety adjustment function in wind power plants should be accomplished only with the simplest electromechanical components to make sure that the system remains fully functional even after a lightning strike. That can be done in a particularly simple and fail-safe manner within the invention by controlling the adjustment rate of one adjusting system as a function of the adjustment distance of the other adjusting system.
For example, it is very simple in this manner to make the effective adjustment rate decrease linearly from an initial maximum value at a rotor blade angle of 0xc2x0 to a lower value, half of the initial maximum value, at a rotor blade angle of 90xc2x0, a trapezoidal curve for the adjustment rate. If one of the two adjusting systems fails in this process, the other adjusting system provides adjustment to a safe feathered position at half the maximum adjustment rate. In case of a failure, only the triangular portion of the trapezoidal adjustment rate curve is cut off. In this manner, the effect of failure of one adjustment system is reduced so much, especially in a wind power plant having a rotor with three blades, each having two independent adjustment systems, that the added loads, particularly those due to aerodynamic imbalance and delayed braking, can be carried by the supporting structure without problems.
It is advantageous to design the means according to the invention such that at least one of the adjusting systems is electrical. It can, as is known at the state of the technology, have an electric gear motor combination in which the output gear meshes with gearing on one ring of the rotatable connection. In particular, very similar designs can be used for both adjusting systems of each rotor blade. That gives a very economical solution because of the mass production effect.
Electrical adjustment systems can advantageously be further designed to provide a monitoring means which at least temporarily increases the adjustment rate of the other adjustment system in case of failure of one of the systems. Electromechanical switches and logical relay switches can be considered a monitoring means. If failure of one adjustment system is detected, the other adjustment system of the pair can be operated briefly at overload, with higher than the nominal adjustment rate, further reducing the effect of a failure. As the adjustment processes involve durations of not more than 30 seconds, such an overload response of the adjusting systems involved is possible without thermal damage.
Furthermore, the electrical adjustment systems can be designed so that the adjustment rate can be changed by stepwise switching batteries feeding the drive on and off. This on and off switching can be done, for example, by electromechanical switches actuated by cams on the other adjustment system. In this case, of course, the switches must be relatively large, as they must switch direct current under load.
That can be avoided by another design in which the adjustment rate is changed by stepwise switching of a stator winding of the drive. For example, the trapezoidal adjustment rate curve can be approximated with three steps in a two-pole stator winding.
According to a further concept of the invention, the drive of one adjustment system has a series-wound motor and the drive of the other adjustment system has a shunt-wound motor. That takes into consideration the situation that the highest possible starting torque is desired for blade adjustment systems, even in battery operation, so that the drive is not stalled by peak wind loads. That corresponds to the behavior of a series-wound machine. On the other hand, the adjustment rate should remain as nearly constant as possible at low loads. That corresponds to the behavior of a parallel-wound machine. The loading of the wind power plant usually decreases relatively rapidly after the adjustment process begins. For that reason, it is particularly advantageous to equip the two adjustment systems operating on the same rotor blade with these two different types of drive motors. It is particularly advantageous to control the series-wound motor in the manner shown above, preferably stepwise, during the adjustment process. The invention also considers providing continuous ramp-shaped control either additionally or alternatively.
It can be particularly advantageous economically for the drive of one adjustment system to have a three-phase motor and the drive of the other adjustment system to have a direct-current motor. The three-phase motor requires use of a frequency converter to accomplish the variable adjustment speed for the control operation. Then for a safety shutdown, a battery is switched to the DC intermediate circuit. That is known at the state of the technology. Depending on the redundancy required, a single inverter can be provided for all the rotor blades, or an inverter for each rotor blade. Such a combined means, in which one three-phase system and one direct-current system can operate on each rotor blade, combines the economic advantage of the three-phase system with the high reliability of the direct-current system.
A further concept of the invention provides that the axes of rotation of the two rotatable connections are at an angle with each other. That can take into consideration the situation that in large wind power plants the bending of the rotor blades under load becomes critical, and it is necessary to counteract the danger of a collision between the rotor blades and the tower due to that. A common help is that of using rotor blades which have, in their unloaded state, pre-curvature directed away from the tower. However, there are structural limits to such pre-curvature. Alternatively, it is possible to give the rotor blades a xe2x80x9ccone anglexe2x80x9d. That is, the rotor blades are angled out of the radial plane of the rotor axis away from the tower. Usual cone angles are between 0.5xc2x0 and 6xc2x0, although substantially larger cone angles can be used in principle. Here, though, there is a major disadvantage that rotor blades set up at a cone angle are stressed during their entire lifetime by additional centrifugal forces and by additional bending moments due to their weight. These act variably during a revolution of the rotor. Furthermore, the projected rotor area decreases as the cone angle increases. That, for example, leads to a power loss of 0.5% at a cone angle of 4xc2x0. However, there is a risk of the rotor blades colliding with the tower only at wind speeds in the vicinity of the nominal wind speed and/or at high wind turbulence.
The mutual angle of the axes of rotation of the two rotatable connections makes it possible to adjust the cone angle of the rotor blade concerned by simultaneous counter-adjustment of the two rotatable connections, without necessarily altering the azimuthal adjustment angle of the rotor blade. Thus the cone angle can be controlled, depending on the prevailing wind conditions, particularly the wind speed and turbulence, such that the energy yield is maximized, the loads on the rotor blades are minimal, and collision of the rotor blades with the tower is still reliably prevented. It is practical to incorporate an integrated cone angle controller in the control system for the wind power plant. For variable-speed wind power plants with the cone angle in the wind direction (downwind coning) in particular, it is possible to compensate, at least partially, for the centrifugal forces of the wind loads caused by the cone angle. That is fundamentally true for wind power plants with rotors on the upwind side as well as on the downwind side.
One embodiment that is particularly favorable with respect to production cost provides that the two rotatable connections are formed by a single live ring roller bearing with three rings and two bearing housings. The rotor hub, bearing rings, rotor blade and adjustment drives can be arranged in many different ways and varied systematically according to the laws of design methodology.
The invention also provides a process for operating the means according to the invention such that the two rotatable connections can be driven with respect to each other to adjust a specified adjustment angle so as to favor distribution of the grease in the rotatable connections. This takes into account the situation that during most of the life of the wind power plant the live ring roller bearing is set into only one or two position ranges, the optimal blade angle and the park position. That makes lubricant supply a problem, because good distribution of the lubricant is best assured by frequent operation with large adjustment paths. This lubrication problem is solved at the state of the technology by the fact that the rotor blades can be adjusted for short times in wind conditions which do not require adjustment of the rotor blades. That, of course, results in decreases in the yield. Now, with the two rotatable connections provided according to the invention, it is possible to move the bearing housings of the rotatable connections of the two adjustment systems with respect to each other without necessarily moving the azimuthal adjustment of the rotor blade in a particularly advantageous manner. This can assure optimal lubricant supply. Alternatively, it is possible to make adjustments temporarily at regular intervals or continuously at very low adjustment rates.
Another suitable potential operation is that of driving the two rotatable connections with respect to each other, adjusting a specified adjustment angle in a manner favoring equal azimuthal load distribution over time. This manner of operation considers the fact that the structural load-bearing parts in the transition region between the rotor blade and the rotor hub, such as the extenders, rotatable connections, and bolt flanges are very unevenly loaded around their periphery because random loads due to rotor thrust are predominantly in one direction, while the periodic weight loads dominate in another direction perpendicular to that. As for the lubrication problem for the rotatable connections, the counteracting adjustment of the rotatable connections equalizes the loads on these parts, allowing a more economical design of the highly loaded bearing structure in the region of the rotor blade roots.
The invention, in all its embodiments, is applicable for all horizontal wind power plants, independently of the number of rotor blades. Its is more economical the smaller the number of blades on the rotor is.